When a vehicle derails, the wheels disengage from the rails, and if an operator is unaware of the derailment, the vehicle continues traveling, resulting in greater damage due to the derailment. Therefore, early detection of derailment and stopping of the vehicle would result in improved safety after derailment occurs.
Various technologies relating to derailment detection were proposed in the past. One of them is a device that uses sensors to measure physical quantities such as acceleration and angular velocity that are applied to the vehicle body, and if signals extracted from the measured values exceed a threshold value, the device determines that a derailment has occurred (e.g., Patent Reference 1-3).
However, in cases where a derailment is detected on the basis of threshold values, differences in the accuracy of derailment detection can occur, depending on the threshold value settings. Thus, there is a problem in that the accuracy of derailment detection can be poor if the threshold values are not set at an optimal value.
In Patent Reference 4, as shown in FIG. 4 (a), there is disclosed a system for restricting the lateral movement of a bogie, provided with a ground-based equipment 11 (referred to below as a “derailment prevention guard”) on an inner side of a pair of rails 4 and a stopper 14 that protrudes downward to the inner side portion of a wheel 13 of a bogie 12. As shown in FIG. 4 (b), in the event of a derailment, this system for restricting the lateral movement of a bogie restricts the movement of the bogie 12 in a lateral direction of the vehicle by having a contact portion 14a of the stopper 14 make contact with an inner side surface of the derailment prevention guard 11.
In Patent Reference 5, as shown in FIG. 5, there is disclosed a derailment and disengagement prevention system, provided with a stopper unit 16 at a lower portion of an axle box 17. In the event that a wheel 13 disengages from a rail 4, this derailment and disengagement prevention system moves a vehicle in a lateral direction of the vehicle, and a sloping member 16a formed on a stopper member 16 makes contact with the rail 4, so that the wheel 13 is positioned outside of the prescribed range of a fastening device 15 of the rail 4.
In Patent Reference 6 there is disclosed a fall prevention device provided with a stopper device 18 disposed at a lower portion of an axle box 17, as shown in FIG. 6. If a derailment occurs, this fall prevention device guides a vehicle so that it travels on a track bed to prevent the vehicle from falling, by causing a stopper piece 18a provided in a stopper device 18 to make contact with a side surface of a rail 4.
However, none of the systems disclosed in Patent References 4-6 detect a derailment. Therefore, it is incumbent on an operator to stop a vehicle after a derailment, but the probability is not zero that the vehicle will continue traveling while the wheels have disengaged from the rails, if the operator is unaware that a derailment has occurred.
On the other hand, in Patent Reference 7 there is disclosed a technology that provides a connecting device for producing electrical signals, and if the connecting device is disconnected, a command is delivered to an alarm device. This technology is provided instead of a vertical displacement detector provided parallel to an axle damper disposed between an axle box support unit and a bogie frame.
However, in the technology disclosed in Patent Reference 7, there are cases in which the connecting device does not become disconnected if a derailment occurs, depending on the durability of the connecting device and the performance of the axle damper. In such cases, a derailment cannot be detected.
In Patent Reference 8, there is disclosed a system for detecting a derailment, wherein a case is immobilized by a portion of a rotating bearing that rotatably supports an axle, and within this case is installed a vibration detector. Detection of a derailment results when a connecting support that connects a base of the vibration detector to a weight part is broken.
However, in the case of the system disclosed in Patent Reference 8, it is difficult to decide on a material, surface area, and shape of the connecting support such that only the connecting support reliably breaks if a derailment occurs. In other words, it is not necessarily the case that it is possible to reliably detect a derailment using the system disclosed in Patent Reference 8.
In Patent Reference 9, there is disclosed a technology for detecting derailment and falling of a railroad vehicle, wherein optical fiber is laid along the outer side of a pair of rails, and detection of derailment and falling of the railroad vehicle occurs when the optical fiber is cut.
However, in the technology disclosed in Patent Reference 9, there are cases in which the fall prevention device disclosed in Patent Reference 6 is installed, and there are cases in which the optical fiber does not break just because of a railway vehicle derailment, due to the position in which the optical fiber is laid. In addition, this technology cannot be considered to be practical, since the optical fiber must be laid along the entire length of track.